Here's a nice looking "whopper of a Manganite group." With an estimated value between $150,000 and $175,000, it has an opening bid of $75,000. It's one of over 300 gems and minerals being auctioned by Heritage.

Ilfeld, Nordhausen, Harz, Thuringia, Germany
If it wasn't for the Ilfeld Manganese mines, Manganite would be relegated to back row status in the Pantheon of Fine Minerals. Fortunately, Manganite was rescued from obscurity by the brilliant, midnight-black crystal groups found in this part of the Harz Mountains. Of the various Manganite groups known, the one seen here is arguably in the top 5. Single crystals run riot over the upper surface of a massive Manganite/Pyrolusite matrix, with thin layers of the original wall rock visible on the absolute bottom of the specimen. Many of the crystals are over one inch, and some are much larger: up to 1.88 inches (4.74 cm). At better than 6.5 inches (16.5 cm) in length, this is not a small example of this mineral; it is a whopper of a Manganite group. The condition of this 'black beauty' is absolutely pristine with no visible damage. As befits a world-class specimen of Ilfeld Manganite, it comes with a custom acrylic base.
Overall Measurements: 6.49 x 3.34 x 2.65 inches (16.5 x 8.5 x 6.74 cm)

I've got my eye on this hunk of heulandite on chalcedony, which "looks like Godzilla as a hockey goalie," and has a current high bid of $1.

Okay, maybe I'm an idiot, but this is one of those facts I'd missed until recently. Despite the impression you may have gotten from grade school and/or old Superman cartoons, diamonds are probably not lumps of coal that just got compressed real good—at least, not in exactly the way you might imagine.

Diamonds are made out of carbon, but the best evidence suggests that they form far more deeply down in the Earth than coal does. Instead of coal being smushed into diamonds, imagine something more like those "grow crystals out of Borax and water" experiments you did in grade school. Only, in this case, the experiment is performed in the fiery depths of Hell, as very un-coal-like atoms of carbon are compressed and heated deep in the Earth's mantle until they start to bond together and grow into a crystalline structure.

Once the crystals are formed, they get to the surface of the Earth via volcanic eruptions.

The really interesting thing about all of this is that it's one of those ideas that's very hard to verify. Diamonds form at a depth we can't go observe directly. All we have to work with is indirect evidence. Because of that, nobody knows exactly where the necessary carbon to make diamonds comes from. This is why the "diamonds are coal" story exists. Some scientists think the carbon is stuff that's existed in the Earth since this planet was formed. Others think it might be coming from terrestrial carbon that got shifted down to the lower levels via plate subduction—although, even then, we're talking about carbon, but not necessarily coal. Read the rest

"My Favorite Museum Exhibit" is a series of posts aimed at giving BoingBoing readers a chance to show off their favorite exhibits and specimens, preferably from museums that might go overlooked in the tourism pantheon. I'll be featuring posts in this series all week. Want to see them all? Check out the archive post. I'll update the full list there every morning.

It's a little funny to think of something that weighs 13.8 pounds being described as a "nugget", but the Fricot Nugget is, in fact, exactly that. "Nugget" in this case, refers to a naturally occurring piece of gold—a precious metal found in its natural habitat. The Fricot Nugget, at the California State Mining and Mineral Museum, is the largest remaining intact mass of crystalline gold from 19th century California. That's a lot of qualifiers, but it's still a big deal. Larger nuggets than this have been found. Heck, larger nuggets than this have been found in California. But most of them ended up melted down. Given the fact that the Fricot Nugget was found in 1865, during the Gold Rush, it's kind of a wonder, in and of itself, that the thing survived intact.

Reader Edie Howe took this photo, and sent me several other photos of the nugget, as well. In one, you can read part of the museum signage that goes with the nugget. Turns out, a big part of why the Fricot Nugget is still with us today is that it was misplaced for several decades, forgotten about in a safe-deposit box. Read the rest